1. Field of the Invention
The present invention relates to a process for the industrial production of propylene oxide by the reaction of propylene with hydrogen peroxide.
2. Related Information
Three routes to propylene oxide (PO) are currently practiced commercially. The oldest art involves the intermediate formation of propylene chlorohydrin by reacting propylene with Cl2/H2O followed by hydrolysis with lime to release the PO and capture the Cl2 as CaCl2. This process is no longer practiced in the U.S. because of the high cost of disposal of the waste CaCl2. An alternative is to use NaOH as the base and to recycle the Na and Cl values by integrating the process with a caustic/chlorine plant:
C3H6+Cl2+H2Oxe2x86x92C3H6(OH)Cl+HCl
C3H6(OH)Cl+HCl+2NAOHxe2x86x92C3H6O+2NaCl+2H2O 
The more recent technologies involve the catalytic oxidation of propylene with t-butyl hydroperoxide (a tertiary hydroperoxide) or xcex2-phenethyl hydroperoxide (a secondary hydroperoxide) to produce PO and co-product alcohols. The hydroperoxides are obtained by catalytic oxidation of isobutane and ethylbenzene respectively:
(CH3)3CH+O2xe2x86x92(CH3)3COOH
(CH3)3COOH+C3H6xe2x86x92C3H6O+(CH3)3COH
and
(C6H5)CH2CH3+O2(C6H5)CH(OOH)CH3(C6H5)CH(OOH)CH3+CH3H6xe2x86x92CH3H6O+(C6H5)CH(OH)CH3
The process economics for these routes are highly dependent on the value of the coproduct alcohols. The first route is practiced by ARCO and Texaco to produce PO and methyl-t-butyl ether wherein the t-butanol (or isobutylene derived from the alcohol) reacts with methanol to produce the ether. Varients of the second route are practiced by Shell and ARCO to produce PO and styrene by dehydrating the xcex2-phenethyl alcohol.
(CH3)3COH+CH3OHxe2x86x92CH3OC(CH3)3+H2O
(C6H5)CH(OH)CH3xe2x86x92(C6H5)CHxe2x95x90CH2+H2O
The search for a single product-direct vapor phase oxidation technology to PO using molecular oxygen continues to be a principal interest of the chemical industry. It is well known that propylene and an active oxygen species such as hydrogen peroxide or an organic hydroperoxide will react over a titanium silicate catalyst, for example as to produce high yields of propylene oxide as shown in U.S. Pat. Nos. 4,833,260 and 4,367,342 which are incorporated herein. In spite of much effort, a catalyst system that gives high selectivity and practical conversion and catalyst life is yet to be developed. For example a recent patent, U.S. Pat. No. 6,031,116 employs a titanium silicalite (TS-1) supported gold catalyst. The highest per pass conversion reported in the cited examples is 0.87 mol % at 92 mol % selectivity to PO. Other examples show that selectivity is in inverse relationship to conversion.
Another single product approach to PO that has been the subject of old and recent art is to oxidize propylene with hydrogen peroxide in a liquid phase in the presence of a titanium silicalite catalyst.
C3H6+H2O2xe2x86x92C3H6+H2O
The hydrogen peroxide is produced by reacting oxygen with a secondary alcohol:
RCH(OH)Rxe2x80x2+O2xe2x86x92H2O2+RC(O)Rxe2x80x2
The coproduct ketone is subsequently reacted with H2 to return the alcohol. The overall net reaction is:
C3H6+H2+O2xe2x86x92C3H6O+H2O
Such a process is described in U.S. Pat. No. 5,523,426 which is incorporated herein. The process disclosed is an integrated epoxidation process of:
(a) reacting a C3-C4 secondary alcohol and molecular oxygen in a liquid phase to form an oxidant mixture comprised of the C3-C4 secondary alcohol, a C3-C4 aliphatic ketone corresponding to the C3-C4 secondary alcohol, and hydrogen peroxide;
(b) separating substantially all of the C3-C4 secondary ketone from the oxidant mixture to provide a concentrated hydrogen peroxide-containing stream comprised of C3-C4 secondary alcohol, hydrogen peroxide, and less than 1 weight percent C3-C4 ketone;
(c) reacting the concentrated hydrogen peroxide-containing stream with a C2-C4 olefin in the presence of a titanium silicalite catalyst and a diluent to form an epoxidation reaction mixture comprised of a C2-C4 epoxide corresponding to the C2-C4 olefin, water, and C3-C4 secondary alcohol;
(d) separating substantially all of the C2-C4 epoxide from the epoxidation reaction mixture to form a crude alcohol stream comprised of water, the C3-C4 secondary alcohol, and less than 1 weight percent of the C2-C4 epoxide; and
(e) recycling at least a portion of the crude alcohol stream for use as at least a portion of the diluent in step (c).
Briefly the present invention discloses an integrated process for the production of propylene oxide comprising:
(a) Reacting isopropanol with oxygen under conditions effective to produce a first reaction product comprising hydrogen peroxide and acetone;
(b) separating and recovering said hydrogen peroxide from said first reaction product;
(c) separating and recovering said acetone from said first reaction product;
(d) reacting said acetone with hydrogen under conditions effective to produce isopropanol;
(e) recycling said isopropanol of step (d) to step (a);
(f) reacting said hydrogen peroxide of step (b) with propylene under conditions effective to produce a second reaction product comprising propylene oxide isopropanol and unreacted propylene;
(g) recovering said second reaction product;
(h) separating and recovering said propylene oxide from said second reaction product;
(i) separating and recovering said isopropanol from said second reaction product and recycling said isopropanol to step (a); and
(j) separating and recovering said propylene from said second reaction product and recycling said propylene to step (f).